The Sea Turtle Resources of the Cocos (Keeling) Islands, Indian Ocean Year 7: 2006
Scott D. Whiting
The Sea Turtle Resources of the Cocos (Keeling) Islands, Indian Ocean Year 7 - 2006 Scientific Consultant Scott D. Whiting Biomarine International PO Box 376u Charles Darwin University Darwin, NT, 0815 Tel./Fax 08 89327607 Mobile 041 3375782 Email
[email protected] Website www.biomarine.com Parks Australia North Staff Cocos (Keeling) Islands Wendy Murray (Government Conservator) Ismail Macrae (Project Officer) Robert Thorn (Senior Ranger) Mohammad Chongkin (Ranger) PO Box 1043 Cocos (Keeling) Islands, Indian Ocean WA, 6799 Tel. 08 91626643 Fax 08 91626680 Conditions of Use This material is copyright © Commonwealth of Australia, except where otherwise indicated. Apart from any use as permitted under the Copyright Act 1968, all other rights are reserved. You may download, store in a cache, display, print and reproduce this material in unaltered form only for your personal, non-commercial use or use within your organisation. You are not permitted to re-transmit, distribute or commercialise the information or material within this report without seeking prior written approval from the Commonwealth. Requests for further authorisation should be directed to the Government Conservator, Cocos (Keeling) Islands, at the above address. ISBN: 0 642 552 967 Acknowledgments This research was funded entirely by Parks Australia North, Cocos (Keeling) Islands. I would like to thank the Parks Australia North staff (Wendy Murray, Ismail Macrae, Robert Thorn and Mohammad Chongkin) for their support both in the field and in the office. Parks Australia North have been forward thinking by initiating sea turtle research even before the National Recovery Plan was finalized. Andrea Koch helped with field work and with the preparation of this report. This project was conducted under a contract with Parks Australia North. Research was conducted under approval from the Animal Ethics Committee at the Charles Darwin University. Several reports on previous research have been submitted to and accepted by the Charles Darwin University Animal Ethics Committee. All photos are by Scott Whiting unless otherwise credited. Cover: Green turtle hatchling – North Keeling Island
CONTENTS INTRODUCTION .................................................................................................................... 1 METHODS ............................................................................................................................. 1 Foraging Turtles............................................................................................................... 1 Capture ......................................................................................................................... 1 Tagging......................................................................................................................... 3 Measurements............................................................................................................... 3 External Examination ................................................................................................... 4 Growth rates ................................................................................................................. 4 Population Estimates .................................................................................................... 4 SCUBA......................................................................................................................... 4 Community Observations............................................................................................. 4 Nesting Turtles.................................................................................................................. 4 North Keeling Island .................................................................................................... 4 Southern Atoll - South Island ...................................................................................... 5 Sand Temperature Loggers .......................................................................................... 5 RESULTS ............................................................................................................................... 6 Foraging Turtles............................................................................................................... 6 Capture Data................................................................................................................. 6 Percentage of Recaptures ............................................................................................. 8 Size Composition ....................................................................................................... 10 Community Sightings................................................................................................. 11 Growth Rates.............................................................................................................. 12 New Recruits .............................................................................................................. 16 Turtle Habitat ............................................................................................................. 17 Fidelity and Movements............................................................................................. 18 Health and Condition.................................................................................................. 18 Genetic Analysis......................................................................................................... 19 SCUBA....................................................................................................................... 20 Other foraging areas investigated............................................................................... 20 Photographs of Historical Sea Turtle Wall................................................................. 22 Nesting Turtles................................................................................................................ 23 North Keeling Island .................................................................................................. 23 Nesting Adults............................................................................................................ 25 Genetic Samples Collected......................................................................................... 25 Hatchlings................................................................................................................... 26 South Island................................................................................................................ 29 Temperature Loggers ................................................................................................. 31 Education........................................................................................................................ 33 Rumah Baru................................................................................................................ 33 Home Island ............................................................................................................... 33 DISCUSSION ........................................................................................................................ 34 Foraging Turtles............................................................................................................. 34 Species Composition .................................................................................................. 34 Size Composition ....................................................................................................... 34 Growth Rates.............................................................................................................. 34 Population Estimates .................................................................................................. 34 New Recruits .............................................................................................................. 35 Health and Condition.................................................................................................. 35 Nesting Turtles................................................................................................................ 35 Conservation Issues ........................................................................................................ 36 REFERENCES ...................................................................................................................... 39
The Sea Turtle Resources of the Cocos (Keeling) Islands – Year 7 Project Report.
INTRODUCTION This is the seventh year of sea turtle research at Cocos (Keeling) Island. In 2006, catch numbers of foraging turtles was increased to ensure more recaptures of previously tagged turtles and also build a larger base of tagged turtles for future years. Additional time was spent on North Keeling Island in 2006 to investigate numbers and nesting success of nesting green turtles. The research at Cocos (Keeling) Islands is achieving results that contribute to the Marine Turtle Recovery Plan (2003). The Cocos (Keeling) Islands are listed as important habitat for marine turtles in the Draft Recovery Plan for Marine Turtles (2005) which will supersede the 2003 plan. This research is also contributing to achieving the objectives of the Indian Ocean Sea Turtle Memorandum of Understanding (IOSEA). Some preliminary results will be presented at the 26th Annual Sea Turtle Symposium in Greece in April 2006. The aims of this study were similar to previous years. The detailed aims of the study this year were to: Continue with the mark-recapture study on the southern atoll with the longterm goal of estimating population size Catch a sample of turtles to continue with the assessment of species composition and size structure From the captured sample, obtain growth rates from previously tagged turtles Continue studies of the nesting turtles on North Keeling Collect genetic material from nesting female turtles The existing project was linked with a project funded by Natural Heritage Trust that used satellite tracking to identify movements of green turtles from their nesting beach on North Keeling. This project will be referred to here but detailed results will be presented in a report produced in June 2006.
METHODS Research methods were similar to those used in previous years but have been summarised below for conciseness (see Whiting 2004a for details).
Foraging Turtles Capture All turtles were captured using the turtle rodeo method (Limpus, 1978) (Figure 1 & Figure 2) in Sectors 5-7 and Sectors 12-13 using a 3.4m dinghy (map Figure 3). Most turtles were brought aboard for measuring and weighing. Large green turtles (over 70 cm curved carapace length) were too heavy to take aboard the small dinghy and were tied to the gunwale of the vessel so they could be tagged and weighed (Figure 4 & Figure 5). Sectors 15 and 18 were investigated as potential capture sites.
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The Sea Turtle Resources of the Cocos (Keeling) Islands – Year 7 Project Report.
Figure 1 The rodeo method of capture
Figure 2 The rodeo method of capture. A green turtle is shown in the yellow circle
Figure 3 SPOT Image of the southern Atoll of the Cocos (Keeling) Islands. The catch Sectors are marked in yellow. This image is used with permission from Department of Transport and Regional Services (DoTRS).
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The Sea Turtle Resources of the Cocos (Keeling) Islands – Year 7 Project Report.
Figure 4 Capture of an adult sized green turtle in sector 6
Figure 5 An adult sized green turtle is held alongside the dinghy for under 10 minutes to allow tagging, measuring and a skin sample to be taken.
Tagging Titanium tags weighing 4.1 g each, were applied to the axial scale of each front flipper (Limpus, 1992). Recaptured turtles from previous years were checked for any injuries sustained from tags. Measurements Measurements of turtles were conducted using standard procedures (Limpus and Reed, 1985). All curved measurements were taken using a flexible fibreglass tape. For green turtles, the curved carapace length (ccl) was measured from the anterior of the nuchal scale, along the mid-line of the carapace to the posterior notch between the two post-central scales. For hawksbill turtles, the curved carapace length was measured to the end of the longest post-central scale. Curved carapace width (ccw) was measured at the widest part of the carapace. Both ccl and ccw had an error of less than +/-0.5 cm. The tail length of large turtles was measured from the carapace to the tip of the tail. Turtles were weighed using a 100 kg (+/-0.5kg) hanging clock-face scale. Small turtles were supported using a rope around each front flipper while large turtles were supported using two ropes around their body. Smaller turtles were either processed in the boat or brought ashore (Figure 6). Large green turtles were tied to the outside of the boat and processed in the water because it was too unsafe to bring them inside the small dinghy (Figure 5).
Figure 6 Several turtles kept in the shade while they are tagged and measured.
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The Sea Turtle Resources of the Cocos (Keeling) Islands – Year 7 Project Report.
External Examination Each captured turtle was examined externally for damage, condition and commensals. Weak turtles were recorded in poor condition if they had low body weight, sunken plastron, sunken eyes or were weak. Turtles were examined for fibropapilloma growths that effect turtles in other study sites around the world. “New Recruits” into the population were recorded as those with distinct external characters which indicated a long period in the open ocean. These included lack of fouling from invertebrate organisms and marine algae, white plastron and a distinct colour difference between the skin on the ventral and dorsal parts of the shoulder. Growth rates The main measurement for growth studies of turtles is either the curved carapace length (ccl) or the straight carapace length (scl), both of which can be estimated from the other. At Cocos Islands, growth rates of sea turtles were measured using cm ccl/ year. Turtles with damage to the carapace that could affect the measurements were not measured. Only growth rates with time intervals of over 11 months were used for analysis Population Estimates Population estimates were calculated using mark-recapture data. These results must be considered preliminary because of the limited number of recaptures. Several methods can be used to estimate population sizes with mark-recapture data, however this preliminary analysis was conducted using Jolly-Seber analysis (Caughley, 1977) and was calculated using Krebs/Win Software (Krebs and Brzustowski, 1998). SCUBA Observations were also conducted during two dives. Dives were conducted offshore from North Point, West Island and near Direction Island. Community Observations Observations from community members were recorded and are listed.
Nesting Turtles North Keeling Island A four day visit was made to North Keeling Island to attach satellite transmitters to nesting female turtles as part of an additional sea turtle project through Natural Heritage Trust. The North Beach on North Keeling was surveyed during three nights (16, 17 and 18 Jan 2006). An initial survey was conducted on the afternoon of 16 January 2006 to count fresh tracks from the night of 15 January 2006 and record tracks previous to this as old tracks. Patrols of the beach were made for at least eight hours each night to intercept nesting green turtles for the tracking project. Once a turtle track was discovered, researchers would follow the track up the beach and stay 4
The Sea Turtle Resources of the Cocos (Keeling) Islands – Year 7 Project Report.
out of sight of the turtle until it had finished nesting or was leaving the beach after a failed nesting attempt. At this time the turtle was tagged, measured and a small skin sample (0.5cm by 0.3cm) was taken. Transmitters for the NHT project were attached after this time. Southern Atoll - South Island A patrol of the southern beaches of South Island was conducted to estimate nesting activity and to retrieve the temperature data loggers positioned in nesting habitat in 2005. Sand Temperature Loggers In 2005, temperature loggers to measure sand temperature were placed in shaded and unshaded locations on North Beach of North Keeling Island and the southern beach of South Island at two depths (10cm and 50cm below the surface). Table 1. Specific Locations of Loggers
Beach North Keeling
Logger Type Shaded
Location 10q 31.286’/105q 40.509’
North Keeling
Exposed in Sun
10q 31.285’/105q 40.511’
South Island South Island
Shaded Exposed in Sun
12q 12.04’ / 096q 54.02’ 12q 12.04’ / 096q 54.02’
Notes Loggers attached to a large coconut tree using white VB cord Loggers attached to a large coconut tree using white VB cord Loggers attached to a tree using VB cord Loggers attached to a tree using VB cord
Figure 7. Temperature loggers attached to a tree using VB cord in 2005.
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The Sea Turtle Resources of the Cocos (Keeling) Islands – Year 7 Project Report.
RESULTS Foraging Turtles Capture Data In 2006, 261 turtles were captured. This comprised 125 (51.0%) green and 120 (49.0%) hawksbill turtles (Table 2). Table 2 Number of each species captured in each year
1999 (Mar) 2000 (Nov) 2002 (Feb) 2003 (Jan) 2004 (Jan) 2005 (Jan) 2006 (Jan) Total
Greens 36 (76.6%) 47 (47.5%) 45 (29.0%) 67 (41.4%) 53 (34.4%) 68 (40.7%) 125 (51.0%) 438 (42.8%)
Hawksbills 11 (23.4) 54 (53.5%) 105 (70.0%) 95 (58.6%) 101 (65.6%) 98 (59.3%) 120 (49.0%) 584 (57.2%)
Total 47 101 150 162 153 167 245 1022
Most turtles were captured in two areas Area 1 (Sectors 5, 6 & 7) and Area 2 (Sectors 12 & 13). A full break down of catch by sectors is shown in Table 1. Individual sectors had different species ratios (Table 3 & Figure 8). Area 1 (Sectors 5,6 & 7) had a higher percentage of green turtles (62%), while Area 2 (Sectors 12 & 13) had a higher percentage of hawksbill turtles (65%) (Table 4).
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The Sea Turtle Resources of the Cocos (Keeling) Islands – Year 7 Project Report.
Table 3 Summary of Species Composition by Sector and year Year
1999
Species
G
1
2 100%
5
H 2000
G H
2002
G
1 16.7% 5 83.3% 1 100%
H 2003
G H
2004
G H
2005
G
3 100%
H 2006
G
5 100%
H Total
G
1 100%
H
10 66.7% 5 33.3%
Sector Area 1 6 31 81.6% 7 18.4% 39 60% 26 40% 31 46.3% 36 53.7% 52 63.4% 30 36.6% 33 54.1% 28 45.9% 48 54.5% 40 45.5% 78 60.9% 50 39.1% 312 58.9% 217 41.1%
Sub Total
Area 2 7
6 100%
1 100%
1 100% 1 12.5% 7 87.5%
12 4 50% 4 50% 8 40% 12 60% 13 20.3% 51 79.7% 10 27.0% 27 73.0% 15 18.5% 66 81.5% 11 20.7% 42 79.3% 29 35.4% 54 64.6% 90 35.1% 256 64.9%
Total
13
10 100%
13 100% 4 9.5% 38 90.5% 4 36.4% 7 63.6% 6 25% 16 75% 10 40.0% 15 60.0% 24 19.8% 99 80.2%
36 76.6% 11 23.4% 47 46.5% 54 51.5% 45 30.0% 105 70.0% 67 41.4% 95 58.6% 53 34.4% 101 65.6% 68 41.0% 98 59.0% 122 51.0% 120 49.0% 438 42.9% 584 57.1%
47
101
150
162
154
166 *
242 #
1022
*Plus one hawksbill was captured in Sect 11. #Plus three green turtles captured in Sect 18.
Table 4 Species Composition by Catch Area
Species 1999 2000 2002 2003 2004 2005 2006 Total
G H G H G H G H G H G H G H G H
Area 1 Sect 5, 6 & 7 31 (81.6%) 7 (18.4%) 39 (54.9%) 32 (45.1%) 32 (43.8) 41 (56.2%) 53 (62.5%) 30 (37.5%) 34 (54.8%) 28 (45.2%) 51 (56.0%) 40 (44.0%) 83 (61.9%) 51 (38.1%) 341 (59.8%) 229 (40.2%)
Area 2 Sect 12 & 13 4 (50.0%) 4 (50.0%) 8 (26.7%) 22 (73.3%) 13 (16.9%) 64 (83.1%) 14 (17.7%) 65 (82.3%) 19 (20.7%) 73 (79.3%) 17 (40.4%) 59 (59.6%) 36 (35.6%) 65 (64.4%) 139 (28.2%) 354 (71.8%)
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The Sea Turtle Resources of the Cocos (Keeling) Islands – Year 7 Project Report.
400 Green
Number of Turtles
350
Hawksbill
300 250 200 150 100 50 0
1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1999 2000 2002 2003 2004 2005 2006 Total Year and Area Figure 8 Species Composition by Year and Area
Percentage of Recaptures Two graphs are shown below which describe the proportion of recaptures to total captures. Figure 9 shows the percentage of recaptures from the total captures for each year individually. For 2006, the proportion of recaptures increased for both green and hawksbill turtles at South Island, although hawksbill recaptures at West Island showed an proportional decrease. It is expected that the increase in total catch in 2006 will increase the recaptures in 2007 in both areas. Figure 10 shows the cumulative recapture rate as a percentage of the overall catch. For example, hawksbill turtles at South Island had a recapture percentage of 25% for 2006 but overall (cumulative) the recapture percentage was around 14%. The proportion of hawksbill recaptures at West Island is above 30%. Additional turtles captured and tagged in 2006 should increase the recapture percentages for green turtles in subsequent years.
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The Sea Turtle Resources of the Cocos (Keeling) Islands – Year 7 Project Report.
Yearly percentage of recaptures - each species and each catch area 60 Green-West Is
50
Hawksbill-West Is
Percentage
Green-South Is
40
Hawksbill-South Is
30 20 10 0 1999
2000
2002
2003
2004
2005
2006
Year
Figure 9 The yearly number of recaptures as a percentage of the yearly total captures.
Cumulative percentage of recaptures - Each species and each catch area 35 30 Percentage
25
Green-West Is Haw ksbill-West Is Green-South Is Haw ksbill-South Is
20 15 10 5 0 1999
2000
2002
2003
2004
2005
2006
Year
Figure 10 The cumulative number of recaptures as a percentage of the cumulative total captures.
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The Sea Turtle Resources of the Cocos (Keeling) Islands – Year 7 Project Report.
Figure 11 Green turtle ready for release
Size Composition Capture In 2006, green turtles ranged in size from 35.5 to 109.5 cm ccl (mean=57.6, sd=14.7, median=55.1, n=125). The size frequency histogram (Figure 12) shows two distinct modal groups, one includes smaller juveniles and the other includes adult sized turtles. Hawksbill turtles ranged in size from 33.0 to 86.3 cm ccl (mean=58.8, sd=14.3, median=62.1, n=120). The size frequency histogram (Figure 13) shows that most turtles were in the 40 to 80 cm ccl size classes.
Size frequency of green turtles 25
Number
20 15 10 5 0 0
10
20
30
40
50
60
70
80
90
Size (cm ccl) Figure 12 Size class frequency of green turtles - 2006
10
100 110 120
The Sea Turtle Resources of the Cocos (Keeling) Islands – Year 7 Project Report.
Size frequency of hawksbill turtles 30
Number
25 20 15 10 5 0 0
10
20
30
40
50
60
70
80
90
100 110 120
Size (cm ccl) Figure 13 Size class frequency of hawksbill turtles - 2006
Size Structure Between Areas The West Island catch area (Area 1) generally contained larger individuals of both species than the South Island catch area (Area 2). For green turtles, Area 1 contained both adult and juvenile sized turtles while area 2 contained only immature sized turtles (see Table 5). For hawksbill turtles, both areas contained both adult and juvenile sized turtles although adult sized turtles were more common in Area 1. Table 5 Size of green and hawksbill turtles by Catch Area
Species Green Hawksbill
Area 1 West 2 South 1 West 2 South
Mean 60.0 52.1 67.7 52.2
Median 58.1 51.8 68.9 50.1
sd 16.8 7.3 10.3 13.2
Range 35.5-109.5 39.1-66.4 39.0-86.3 33.0-83.3
n 83 39 51 69
Community Sightings One community report was submitted during the sea turtle surveys in 2006. The report [with photograph attached (Figure 14)] was by Karen Wilshaw (Undersea Reflections). This is the first photographically confirmed sighting of a loggerhead (Caretta caretta) turtle at Cocos (Keeling) Islands.
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The Sea Turtle Resources of the Cocos (Keeling) Islands – Year 7 Project Report.
Figure 14. A loggerhead turtle (Caretta caretta) observed and photographed by Karen Wilshaw Undersea Reflections www.underseareflections.com
Growth Rates In 2006, growth rates were obtained for seven green turtles and 31 hawksbill turtles. These growth rates have been added to previous growth data to provide a total summary of growth rates in different size classes. A summary of growths rates for each 10 cm size class is presented in Table 6 & Table 7. In 2006, like other years, there were fewer recaptures of green turtles than hawksbill turtles. However, in 2006 a higher percentage of green turtles were recaptured than in any other year. Seven green turtles growth rates were obtained from recaptured individuals. This is more than redouble the recapture rate from 2005. Combining all years, green turtles had a mean growth rate of 6.7 cm ccl/yr for 14 turtles within the size range of 40 to 80 cm ccl. The fastest individual growth rate was 9.3 cm/yr ccl (60-70 cm size class) and the slowest was 3.8 cm ccl/yr (80-90 cm size class). In 2006, a total of 31 recaptures was made of previous tagged hawksbill turtles (25% of all captures) bringing the total growth rates obtained for this species to 114. Using all growth rates, hawksbill turtles had an overall mean growth rate of 3.6 cm ccl for turtles in the 30 to 90 cm ccl size range (n=114). The mean growth rate varied from 1.0 cm ccl (80-90 cm size class) to 6.0 cm ccl (30-40 cm size class). The fastest growth rate for an individual hawksbill turtle was 8.3 cm ccl/yr (30-40 cm size class) and the slowest was 0.1 cm ccl/yr (70-80 cm size class). Individual growth rates are shown in Figure 15 and Figure 16.
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The Sea Turtle Resources of the Cocos (Keeling) Islands – Year 7 Project Report.
Table 6 Mean Growth Rates of Green Turtles by Mean Size Class (10cm increments) (all years)
Mean Size Class mean 4.9 7.0 7.5 3.8 6.7
40-50 50-60 60-70 70-80 80-90 Total
Growth Rate cm ccl/yr sd range 0.1 4.9- 5.0 1.2 5.7-8.5 1.8 5.7-9.3 1.7 3.8-9.3
n 2 6 3 1 14
Table 7 Mean Growth Rates of Hawksbill Turtles by Mean Size Class (10cm increments) (all years)
Mean Size Class 30-40 40-50 50-60 60-70 70-80 80-90 Total
Growth Rate cm ccl/yr mean sd Range 6.9 1.9 3.5-8.3 5.2 1.3 2.0-7.1 4.0 1.7 0.6-7.3 3.2 1.2 1.4-5.8 1.8 1.0 0.1-3.4 1.0 0.8 0.0-2.0 3.6 1.9 0.1-8.3
n 5 18 38 25 23 5 114
Growth rates cm/yr ccl
Growth rates for green turtles - all years 10 8 6 4 2 0 40
50
60
70
80
90
Size cm ccl Figure 15 Individual growth rates of green turtles (Length)
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The Sea Turtle Resources of the Cocos (Keeling) Islands – Year 7 Project Report.
Growth rates for Hawksbill Turtles - All Years
growth rate cm/yr ccl
10 8 6 4 2 0 -2
30
40
50
60
70
80
90
Size cm ccl Figure 16 Individual growth rates of hawksbill turtles (Length)
Growth rates of individuals vary through and between each other. Figure 17 shows the growth rates of individual turtles through time for those with three or more captures. The steeper the slope of the line the faster the growth of the turtle and the flatter the line the slower the growth rate. It is interesting to note that growth rates varied between individuals of the same size. For example, in Figure 17, Turtle CA4401 and CA4647 were both captured on the 10 January 2002. Three years later CA4401 was 74.9 cm ccl but CA4647 took four years to reach 72.0 cm ccl. Similarly, CA4625 was smaller than CA7900 in January 2004 but by January 2006 CA4625 was 5 cm larger.
Size of hawksbill turtles through time 90 Size of turtle (cm ccl)
80 70 60 50 40 30 20 10 0 2-Jan-2006
2-Jan-2005
2-Jan-2004
2-Jan-2003
1-Jan-2002
1-Jan-2001
1-Jan-2000
1-Jan-1999
CA7437 CA7458 CA4240 CA4330 CA4342 CA4384 CA4401 CA4420 CA4499 CA4580 CA4625 CA4647 CA4651 CA4661 CA7431 CA7523 CA7900
Date of capture Figure 17 Size of hawksbill turtles through time. Only turtles with three or more captures are shown. Numbers represent tag numbers of turtles.
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The Sea Turtle Resources of the Cocos (Keeling) Islands – Year 7 Project Report.
Figure 18 shows more clearly how individual turtles may have different growth rates at different size classes but also how the individual rates may be different for the norm for that size class. For example CA7431 and CA7900 showed slow growth rates for both intervals when compared to other turtles of similar size. Turtles CA4342 and CA4420 had growth rates that slowed down to near zero growth for the second interval. Turtle CA4330 showed variable growth rates over several intervals even though the size range did not change.
Consecutive growth rates for individuals CA7437
Growth Rate (cm/yr ccl)
7
CA7458 CA4240
6
CA4330 CA4342
5
CA4384
4
CA4401 CA4420
3
CA4499 CA4580
2
CA4625
1
CA4647 CA4651
0
CA4661
30
40
50
60
70
80
90
CA7431 CA7523
Size (cm ccl)
CA7900
Figure 18 Consecutive growth rates of individual turtles by size.
Population Estimates Jolly-Seber Mark Recapture Population estimates for hawksbill turtles at South Island and West Island are shown in Table 8 & Table 9. These tables show the number of recaptures in each year and the initial year of capture. The population estimates are shown for catch Area 1 (West Island) and for Catch Area 2 (South Island) (Table 10). Using all years, the mean population estimate for West Island Catch Area (Area 1) was 406 with a density of 89 hawksbills / km2. The South Island Catch Area (Area 2) had a mean of 410 hawksbills and a density of 85 hawksbills / km2. Table 8 Total captures and recaptures of hawksbill turtles in West Island sectors (Sect 5, 6 & 7)
1999 2000 2002 2003 2004 2005
1999 7
2000 32
1999
2000
Hawksbills – West Island Total Turtles Captured by Year 2002 2003 2004 2005 36 30 28 44 2002 14 6
2003 2 1 9
2004 0 3 7 0
2005 1 3 4 1 5
2006 51 2006 0 1 4 3 5 9
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The Sea Turtle Resources of the Cocos (Keeling) Islands – Year 7 Project Report.
Table 9 Total captures and recaptures of hawksbill turtles in South Island sectors (Sect 12 & 13).
1999 4
2000 22
1999
2000
1999 2000 2002 2003 2004 2005
Hawksbills – South Island Total Turtles Captured by Year 2002 2003 2004 2005 54 65 73 59 Year of Recapture 2002 2003 2004 2005 1 0 0 0 0 0 5 5 3 11 7 5
2006 65 2006 0 1 2 4 3 6
Table 10 Population estimates of hawksbill turtles at West and South Island
Estimate #
Population Estimate
1 2 3 4 5 Mean (se)
Min. 255 53 179 88 127 140
West Island Estimate 1234 64 369 145 218 406
Max. 14037 90 1137 324 522 3222
Min. 36 86 191 364 193 174
South Island Estimate 265 378 354 678 374 410
Max. 9038 5610 970 1803 1119 3708
New Recruits Four green turtles were classified as new recruits to the foraging population in 2006 (Table 11). Table 11. Size range of new recruit green turtles based on external examination in the field
Year 1999 2001 2002 2003 2004 2005 2006
Size of new recruit (cm ccl) mean ccl sd range
44.0 42.2 46.9 43.7 39.3
4.15 6.39 1.13 2.7
37.9 – 46.2 41.2 – 58.6 42.3-45.5 35.5-41.3
N 0 0 1 3 6 4 4
No hawksbill turtles were identified as new recruits from external examination. Identifying hawksbill new recruits is more difficult than green turtles because of their natural yellow colouration. In 2006, 14 of the captured hawksbill turtles were under 40 cm ccl which could provide a measure of new recruits (see discussion in Whiting 2004a).
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The Sea Turtle Resources of the Cocos (Keeling) Islands – Year 7 Project Report.
Figure 19. New Recruit – Ventral side (Photo by A. Koch)
Figure 20. New Recruit – Dorsal side (Photo by A. Koch)
Table 12 Number of green and hawksbill turtles in the small size classes
Year 1999 2001 2002 2003 2004 2005 2006
Greens #
